Billabong BTS Plaid 70’s Bottom- Everything is right about the Back to School (BTS) Plaid 70’s bottom by Billabong. From the adjustable side ties to the incredible print and ruffles across the top seam I don’t think anyone could ask for more. Don’t look hard for the latest greatest, Billabong has taken style that worked in the 1970’s and made the modern updates for the perfect combination just for you.